Ultra-light mineral foam

ABSTRACT

A process for the production of a mineral foam includes separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry includes water and Portland cement as well as calcium silicate hydrate crystallization seeds; contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; and casting the slurry of foamed cement and leave it to set.

The present invention refers to an ultra-light mineral foam with a baseof Portland cement, to a process for production of such mineral foamsand to elements of construction comprising these foams.

Generally, a mineral foam, in particular a cement foam, is veryadvantageous for many applications due to its properties, such as itsthermal insulation properties, its acoustic insulation properties, itsdurability, its resistance to fire and its easy implementation.

A mineral foam is a material in the form of a foam. This material isgenerally more lightweight than typical concrete due to its pores orempty spaces. These pores or empty spaces are due to the presence of airin the mineral foam and they may be in the form of bubbles. Anultra-light foam is understood to be a foam generally having a densityin its dry state of between 20 and 300 kg/m³.

When a mineral foam is poured into an element, the mineral foam maycollapse due to a lack of stability in the mineral foam, for exampleduring its placing or before it sets. Such problems may be due tocoalescence phenomena, to Ostwald ripening phenomena, to hydrostaticpressure or to draining phenomena, the latter being greater inparticular in case of elements of important height.

The difficulty in the production of mineral foams is therefore toproduce a stable mineral foam which reduces these collapse problems.However, known processes for providing sufficiently stable mineral foamsrequire cement compositions that comprise numerous additives and thatare difficult and costly to realize.

In U.S. Pat. No. 5,696,1741 the simultaneous use of (i) cationic and(ii) anionic components has already been proposed for obtaining mineralfoams. Such cementitious foams comprise ammonium stearates as theanionic component and a cationic component denominated Arquad T.

The application WO 2013/150148 describes mineral foams based on cementcomprising different admixtures. These foams may comprise calciumaluminate cement in order to allow a rapid setting, or fine mineralcomponents in addition to Portland cement. Nevertheless, the lowestdensity achieved with this process is mostly limited to 100 kg/m³.

The patent application WO 2011/086333 describes mineral foams based onaluminous cements. The high reactivity of these cements certainly allowsthe formation of stable and homogenous mineral foams, but the high costsand the high reactivity result in that this invention is in very manycases difficult to use by the user.

In order to meet user requirements, it has become necessary to find aformulation for an ultra-light and highly stable mineral foam, therealisation of which is simple and incurs little cost.

Further, the problem which the invention intends to solve is to find aformulation for a stable and ultra-light mineral foam, which does notcollapse when the foam is poured vertically and the realisation of whichis relatively effortless and incurs little cost.

The invention relates to a process for the production of a mineral foamcomprising the following steps:

-   -   (i) separately preparing a slurry of cement and an aqueous foam,        wherein the cement slurry comprises water (W) and Portland        cement (C) as well as calcium silicate hydrate (CSH)        crystallization seeds;    -   (ii) contacting the slurry of cement with the aqueous foam to        obtain a slurry of foamed cement;    -   (iii) casting the slurry of foamed cement and leave it to set.

According to another feature of the invention, a mineral foam isprovided that is obtained or obtainable by the inventive process. Thefoam according to the invention may be used as construction material orinsulating material. For example, the mineral foam may be poured betweentwo panels of gypsum boards, or between two brick walls or between twoload-bearing concrete walls.

The invention also relates to elements of construction comprising amineral foam according to the invention.

The process provided by the present invention has one or more of thefollowing characteristics:

-   -   the process is universal, which is to say it makes it possible        to produce a stable mineral foam from any type of cement;    -   the process is easy to implement;    -   the process can be easily transported to any site or jobsite;    -   the process makes it possible to implement a mineral foam in a        continuous manner. It is therefore possible to produce the        mineral foam continuously and to pour this foam without        interruption.

The process for production of a mineral foam according to the inventionmay be used in a discontinuous or continuous system.

The mineral foam provided by the instant invention has one or more ofthe following characteristics:

-   -   the mineral foam according to the invention has excellent        stability properties. In particular, it is possible to obtain        foam that does not collapse or only very slightly when the foam        is poured vertically or from a considerable height. For example,        the mineral foam according to the invention does not collapse or        only very slightly when it is poured vertically from a height        greater than or equal to 2 metres;    -   the mineral foam according to the invention has excellent        thermal properties, and in particular very low thermal        conductivity. It is highly desirable to reduce thermal        conductivity in construction materials since this makes it        possible to obtain savings of heating energy for residence and        office buildings. Furthermore, this decrease makes it possible        to reduce thermal bridges, in particular in the construction of        buildings several stories high and designed using indoor thermal        insulation. In particular thermal bridges are reduced on the        intermediary floors.

Cement is a hydraulic binder comprising at least 50 wt.-% of CaO and ofSiO₂. Cement may therefore contain other components in addition to CaOand SO₂, in particular slag, silica fume, pozzolans (natural andcalcined), fly ash (siliceous and calcic) and/or limestone.

Portland cement as used in the invention may be any type of Portlandcement, whatever its chemical composition is, and in particular whateverits alkaline content is. Therefore, one of the advantages of theinvention is not having to select a specific type of Portland cement.Advantageously, the Portland cement used in the invention is selectedfrom the cements readily available on the market.

The suitable cement used in step (i) of the invention is preferably thecements described according to the European NF EN 197-1 Standard ofApril 2012 or mixtures thereof, preferably cement of the types CEM I,CEM II, CEM III, CEM IV or CEM V.

The water/cement ratio (wt/wt ratio) of the cement slurry prepared instep (i) is preferably from 0.25 to 0.5, more preferably from 0.28 to0.35, in particular 0.29. The water/cement ratio may vary, for exampledue to the water demand of the mineral particles when these are used.The water/cement ratio is defined as being the ratio by mass of thequantity of water (W) to the dry Portland cement mass (C).

The cement slurry prepared in step (i) may comprise a water reducer,such as a plasticiser or a super-plasticiser. A water reducer makes itpossible to reduce the amount of mixing water for a given workability bytypically 10-15%. By way of example of water reducers, mention may bemade of lignosulphonates, hydroxycarboxylic acids, carbohydrates, andother specific organic compounds, for example glycerol, polyvinylalcohol, sodium alumino-methyl-siliconate, sulfanilic acid and casein asdescribed in the Concrete Admixtures Handbook, Properties Science andTechnology, V. S. Ramachandran, Noyes Publications, 1984.

Super-plasticisers belong to a new class of water reducers and arecapable of reducing water contents of mixing water, for a givenworkability, by approximately 30% by mass. By way of example of asuper-plasticiser, the PCP super-plasticisers without an anti-foamingagent may be noted. The term “PCP” or “polyoxy polycarboxylate” is to beunderstood according to the present invention as a copolymer of acrylicacids or methacrylic acids and their esters of polyoxy ethylene (POE).

Preferably, the cement slurry comprises 0.05 to 1%, more preferably 0.05to 0.5% of a water reducer, a plasticiser or a super-plasticiser,percentage expressed by mass relative to the dry cement mass.

Preferably, the cement slurry does not comprise an anti-foaming agent,or any agent having the property of destabilizing an air/liquidemulsion. Certain commercial super-plasticisers may contain anti-foamingagents and consequently these super-plasticisers are not suitable forthe cement slurry used to produce the mineral foam according to theinvention.

Preferably, the cement slurry used to produce the mineral foam accordingto the invention comprises 0.05 to 2.5 wt.-% of an accelerator,expressed as dry mass relative to dry cement mass.

According to an embodiment of the invention, other additives may beadded to the cement slurry or the aqueous foam. Such additives may bethickening agents, viscosifying agents, air entraining agents, settingretarders, coloured pigments, hollow glass beads, film forming agents,hydrophobic agents or de-polluting agents (for example zeolites ortitanium dioxide), latex, organic or mineral fibres, mineral additionsor their mixtures. Preferably, the additives do not comprise anydefoaming agents.

The expression “thickening agent”, is generally to be understood as anycompound making it possible to maintain the heterogeneous physicalphases in equilibrium or facilitate this equilibrium. The suitablethickening agents are preferably gums, cellulose or its derivatives, forexample cellulose ethers or carboxy methyl cellulose, starch or itsderivatives, gelatine, agar, carrageenans or bentonite clays.

According to an embodiment of the invention, the cement slurry used toproduce the mineral foam according to the invention may further comprisemineral particles. Preferably, the cement slurry used to produce themineral foam according to the invention may comprise 0 to 50% of mineralparticles, more preferably from 5 to 40%, most preferably from 5 to 35%,the percentages being expressed by mass relative to the mass of slurryof foamed cement.

The suitable mineral particles are selected from calcium carbonate,silica, ground glass, solid or hollow glass beads, glass granules,expanded glass powders, silica aerogels, silica fume, slags, groundsedimentary siliceous sands, fly ash or pozzolanic materials or mixturesthereof.

The mineral particles used according to the invention may be slags (forexample, as defined in the European NF EN 197-1 Standard of April 2012,paragraph 5.2.2), pozzolanic materials (for example as defined in theEuropean NF EN 197-1 Standard of April 2012, paragraph 5.2.3), fly ash(for example, as described in the European NF EN 197-1 Standard of April2012, paragraph 5.2.4), calcined schists (for example, as described inthe European NF EN 197-1 Standard of April 2012, paragraph 5.2.5),material containing calcium carbonate, for example limestone (forexample, as defined in the European NF EN 197-1 Standard paragraph5.2.6), silica fume (for example, as defined in the European NF EN 197-1Standard of April 2012, paragraph 5.2.7), siliceous additions (forexample, as defined in the “Concrete” NF P 18-509 Standard), metakaolinor mixtures thereof.

Fly ash is generally pulverulent particles comprised in fume fromthermal power plants which are fed with coal. Fly ash is generallyrecovered by electrostatic or mechanical precipitation.

Slags are generally obtained by rapid cooling of molten slag resultingfrom melting of iron ore in a blast furnace.

Silica fume may be a material obtained by the reduction of very purequality quartz by the coal in electric arc furnaces used for theproduction of silicon and alloys of ferrosilicon. Silica fume isgenerally formed of spherical particles comprising at least 85% by massof amorphous silica.

The pozzolanic materials may be natural siliceous and/orsilico-aluminous materials or a combination thereof. Among thepozzolanic materials, natural pozzolans can be mentioned, which aregenerally materials of volcanic origin or sedimentary rocks, and naturalcalcined pozzolans, which are materials of volcanic origin, clays, shaleor thermally-activated sedimentary rocks.

According to the invention, CSH crystallization seeds are contained inthe cement slurry prepared in step (i). Preferably, the CSHcrystallization seeds comprise calcium silicate hydrate particles.Preferably, the CSH crystallization seeds are present in the form of anaqueous suspension.

The CSH crystallisation seeds may be present in an amount of 0.5-7% indry CSH by weight of the dry Portland cement, preferably 0.5-5% in dryCSH by weight of the dry Portland cement, more preferably 0.7-3% in dryCSH by weight of the dry Portland cement.

Preferably the CSH crystallization seeds have a D90 of less than 5 μm.

It has been found that the addition of CSH crystallization seeds to thecement slurry has a stabilizing effect on Portland cement based mineralfoams and thus allows the production of ultra-low density mineral foams,whereby the stabilizing effect is independent from the type of Portlandcement used. Therefore, the invention allows a broad choice of variousPortland cement types.

A further advantage of the invention is that the use of CSHcrystallization seeds allows to manufacture a stable foam from Portlandcement without the need of adding ultra-fine limestone particles.

Further, it has been observed that the average diameter of the bubblesof the slurry of foamed cement is decreasing when using CSHcrystallization seeds in the cement slurry.

Even though the exact mechanism of action of the CSH crystallizationseeds in the inventive process has not been completely analysed yet, itis understood that the improved stability of the foam is the results oftwo phenomena that occur in the mineral foam:

-   -   improved stabilisation of the mineral foam before the cement        slurry sets by a Pickering stabilization effect due to the small        size of the CSH crystallization seeds;    -   improved stabilisation of the mineral foam through the        acceleration of the setting of the slurry by the CSH        crystallization seeds. CSH crystallization seeds are indeed        currently foremost used in concrete applications for their        accelerating effect, and the use of accelerators is beneficial        to the stability of the foams. Indeed, upon mixing of the cement        slurry and the foam, the foam is in a plastic state and must be        able to support its own weight until the cement sets.

CSH crystallization seeds have become known as accelerator additives incementing applications. In particular, the surface of calcium silicatehydrate (CSH) nano-particles added to the cement slurry is used tostimulate the development of calcium silicate hydrate nucleiefficiently.

CSH crystallization seeds can be purchased from BASF under the productname X-Seed®, but as such this product is not suitable for thisinvention, because it contains defoaming agents.

The CSH crystallization seeds used in this invention may be produced byvarious methods, such as from the following sources:

-   1. A laboratory produced batch of diluted CSH seeds by precipitation    of CSH from calcium nitrate and sodium silicates:

200 mL of a sodium silicate solution with a solids content of silicateof 40%, 400 mL water and 2 g of a water reducer that does not have anydefoaming effects are weighed into a reactor. Then, 200 mL of a 50%solution of a calcium salt, such as a calcium nitrate, is added into thereactor within 30 seconds while stirring at 1200 rpm. An instantaneousreaction is observed and CSH seeds are obtained that are present in a22% solution.

-   2. Hydrated cement pastes produced in the laboratory:

The equipment used for the production of a gel of hydrated cement is aglass reactor having a content of approx. 2 L, the water-proof lidthereof being equipped with an electrically driven stirrer. The rotorblade of the stirrer is of the anchor type that allows to stir at thebottom of the reactor in order to prevent the depositing of a sediment.

For the preparation of 1.5 L of a gel of hydrated cement, the followingprocedure is observed:

-   -   Introduction of 1.5 L of a super-plasticiser (such as 20 g of        Mater Glenium ACE456 by BASF) suitable for accelerating the        hydration process,    -   Controlled stirring at 450 rpm,    -   Addition of 200 g of cement (typically CEM I 52.5R from Port La        Nouvelle of LafargeHolcim),    -   Stirring at 450 rpm during 48 hours without stopping,    -   After 48 hours of stirring, retrieving the obtained solution and        storing the same in a suitable canister closed tightly        (typically a 2 litres polypropylene canister),    -   Allowing the canister to rest during several days (minimum 3        days, preferably 7 days).

The gel of hydrated cement is comprised of free water, various hydrationproducts, among them a gel of calcium silicate hydrate (CSH),portlandite and anhydrides of non hydrated cement. The gel of hydratedcement is used as is and constitutes a solids content of 15-20 wt.-%after loss on ignition at 60° C./72 hours.

-   3. Sedimentation sludge obtained from fresh concretes or mortars:

Sedimentation sludge is collected from sedimentation tanks that are usedin waste water management installations of concrete productionfacilities. Therefore, such sludge may originate, e.g., fromsedimentation tanks of ready mix concrete plants, in which washing waterfrom concrete transportation trucks is collected. The sludge ispreferably collected by means of a shovel loader, and preferably fromthe back of a second tank, because this would contain less sand andfiner particles.

The humid sludge is sieved in water at 200 μm and the fraction having aparticle size of less than 200 μm is collected and stored in tanks orbuckets and sedimentation is allowed. After sedimentation the surfacewater is removed by suction. A dispersant (super-plasticiser) not havingdefoaming effects is added to the sediment at an amount of 0.1 wt.-%(dry) of the total dry mass of the sediment, while mixing at high speed(2000 rpm) in a Rayneri Turbotest mixer. The final product has a solidscontent of 20-30 wt.-% and is mainly composed of CSH seeds.

The formulation of the invention overcomes the technical prejudiceaccording to which the use of various additives is necessary in order toensure the stability of the mineral foam.

In particular, the mineral foam obtained by the invention issubstantially free of fine particles, i.e. no fine particles are addedon top of the small fraction of finer particles typically included inordinary Portland cement. The term “fine particles” is understood tocomprise particles, the mean diameter D50 of which is below 2 μm. TheD50 diameter corresponds to the 50^(th) percentile of the distributionby volume of the particle size, i.e. 50% of the volume is formed byparticles having a size that is below the D50 diameter and 50% having asize that is above the D50 diameter. The term “substantially” means lessthan 1%, preferably less than 5%, expressed in mass in relation to thecement mass.

Cements that are less or not suitable for the realisation of theinvention are calcium aluminate cements and their mixtures. Calciumaluminate cements are cements generally comprising a mineral phaseC4A3$, CA, C12A7, C3A or C11A7CaF₂ or their mixtures, such as, e.g.,Ciment Fondu® (a calcium aluminate-based hydraulic binder), aluminacements, sulfoaluminate cements and calcium aluminate cements accordingto the European NF EN 14647 Standard of December 2006. Such cements arecharacterized by an alumina (Al₂O₃) content of 35 wt.-%.

In step (i), the slurry may be prepared using mixers typically used toproduce cement slurries. They may be a mixer for slurries, a mixer froma cement batching plant, a mixer described in the European NF EN 196-1Standard of April 2006—Paragraph 4.4, or a beater with a planetarymovement.

According to a first mode of operation, the cement slurry may beprepared by introducing into a mixer water, the solution of CSHcrystallization seeds and optionally additives (such as a waterreducer). Thereafter, the Portland cement, and optionally otherpulverulent components, is added into the mixer. The paste that isobtained in this way is then mixed for obtaining the cement slurry.Preferably, the cement slurry is kept under agitation for example bymeans of a deflocculating paddle at a speed which may be between 1000and 600 rpm, depending on the volume of the slurry, during the entiremanufacturing process.

According to a second mode of operation, the cement slurry may beprepared by introducing a part of the water, the CSH crystallizationseeds and optionally the additives (such as a water reducer) in a mixer,and then the cement and afterwards the further components.

According to a third mode of operation, the cement slurry may beprepared by introducing into a mixer the cement, and eventually all theothers pulverulent components. The cement and the pulverulent componentsare mixed in order to obtain a homogenous mixture. Water, the CSHcrystallization seeds and optionally the additives (such as a waterreducer) are then introduced into the mixer.

According to a forth mode of operation, the cement slurry is prepared ina continuous way by preparing in advance a mixture containing water, CSHcrystallization seeds and optionally additives (such as a waterreducer).

In step (i), the aqueous foam may be produced by combining water and afoaming agent, then introducing a gas. This gas is preferably air. Thefoaming agent is preferably used in an amount of 0.25-5.00 wt.-%,preferably 0.75-2.50 wt.-%, (dry mass) of the mass of water.

The introduction of air may be carried out by stirring, by bubbling orby injection under pressure. Preferably, the aqueous foam may beproduced using a turbulent foamer (bed of glass beads for example). Thistype of foamer makes it possible to introduce air under pressure into anaqueous solution comprising a foaming agent.

The aqueous foam may be generated continuously in the process accordingto the invention.

The generated aqueous foam has air bubbles with a D50, which is lessthan or equal to 400 μm, preferably comprised from 100 to 400 μm, morepreferably comprised from 150 to 300 μm. Preferably, the generatedaqueous foam has air bubbles with a D50 which is 250 μm.

The D50 of the bubbles is measured by back scattering. The apparatusused is the Turbiscan® Online provided by the Formulaction company.Measurements of the back scattering make it possible to estimate a D50for the bubbles of an aqueous foam, by knowing beforehand the volumefraction of the bubbles and the refractive index of the solution offoaming agent.

Preferably, the foaming agent is an organic protein derivative of animalorigin (such as, e.g., the foaming agent named Propump26, a powder ofhydrolysed keratin, sold by the company Propump Engineering Ltd) or ofvegetable origin. The foaming agents may also be a cationic surfactant(for example cetyltrimethylammonium bromide, CTAB), an ionic surfactant,an amphoteric surfactant (for example cocamidopropyl betaine, CAPB), ora nonionic surfactant, or mixtures thereof.

In step (ii), the cement slurry may be homogenized with the aqueous foamby any means to obtain a slurry of foamed cement. Preferably, step (ii)of the process according to the invention may comprise the introductionof the cement slurry and the aqueous foam into a static mixer to obtaina slurry of foamed cement.

The suitable static mixers preferably have elements in the form of apropeller to ensure complete radial mixing and successive divisions ofthe flow for each combination of liquids and gas. The suitable staticmixers according to the invention preferably have helical elements whichtransmit a radial speed to the fluid, which is directed alternativelytowards the side of the mixer, then towards its centre. The successivecombinations of elements directing the flow clockwise and counterclockwise provoke a change of direction and a division of the flow.These two combined actions increase the efficiency of the mixing.Preferably, the static mixer used in the process according to theinvention is a mixer operating by dividing the continuous flow of cementslurry and of aqueous foam. The homogeneity of the mix is based on thenumber of divisions. According to the process of the invention, 16elements are preferably used to ensure good homogeneity. The suitablestatic mixers according to the process of the invention are preferablythose commercialised under the brand name of Kenics®.

According to a more particular embodiment, the cement slurry is pumpedat a precise volume flow, which is a function of the target compositionof foamed cement slurry. Then, this cement slurry is combined with theaqueous foam already circulating in the circuit of the process. Theslurry of foamed cement according to the invention is thus generated.This slurry of foamed cement is cast and left to set.

Advantageously, the inventive process does not need neither an autoclavestep, nor a thermal treatment step (for example at 60-80° C.) in orderto obtain a cement foam according to the invention.

The invention also relates to a slurry of foamed cement as obtained instep (ii) of the process of the invention.

Further, the invention also relates to a mineral foam obtained accordingto the process of the invention.

Further, the invention also relates to a mineral foam obtainableaccording to the process of the invention.

The mineral foam of the invention may be prefabricated. The mineral foamaccording to the invention may also be directly prepared on the jobsiteby installing a foaming system on the jobsite.

Preferably, the mineral foam according to the invention may have adensity of 20 to 300 kg/m³, more preferably from 20 to 150 kg/m³, mostpreferably from 30 to 80 kg/m³. Even more preferably the mineral foamaccording to the invention may have a density of 20 to 70 kg/m³, morepreferably 20 to 60 kg/m³, most preferably 20 to 50 kg/m³. It is to benoted that the density of the slurry of foamed cement (humid density) isdifferent to the density of the mineral foam (density of the hardenedmaterial).

The invention provides another advantage in that the mineral foamaccording to the invention has excellent thermal properties, and inparticular very low thermal conductivity. Thermal conductivity (alsocalled lambda (λ)) is a physical value characterizing the behaviour ofmaterials during the transfer of heat by conduction. Thermalconductivity represents the quantity of heat transferred per unit ofsurface and per unit of time submitted to a gradient of temperature. Inthe international system of units, thermal conductivity is expressed inwatts per metre Kelvin (W/m·K). Typical or conventional concretes havethermal conductivity values measured at 23° C. and 50% relative humidityof 1.3 to 2.1. The thermal conductivity of the mineral foam according tothe invention may be from 0.030 to 0.150 W/m·K, preferably from 0.030 to0.060 W/m·K, more preferably from 0.030 to 0.055 W/m·K, the margin oferror being ±0.4 mW/m·K.

Preferably, the mineral foam according to the invention has a very goodfire resistance.

The mineral foam according to the invention may be a concrete, which ispre-cast on the jobsite, a ready-mix concrete or a concrete produced ata production plant of pre-cast elements. Preferably, the mineral foamaccording to the invention is a ready-mix concrete.

The invention also relates to an element of construction comprising themineral foam according to the invention.

The invention also relates to the use of the mineral foam according tothe invention as construction material.

The mineral foam according to the invention may be used to cast walls,ceilings and roofs during a jobsite. It is also possible to realiseprefabricated elements in a prefabrication plant, such as blocs orpanels.

The invention also relates to the use of the mineral foam according tothe invention as insulating material.

Advantageously, the mineral foam according to the invention makes itpossible in certain cases to replace glass wool, mineral wool orpolystyrene insulating material.

Advantageously, the mineral foam according to the invention may be usedto fill empty or hollow spaces in a building, a wall, a partition wall,a brick, a floor or a ceiling. In this case, it is used as a fillingcompound. Such composite construction elements also constitute objectsof the invention per se.

Advantageously, the mineral foam according to the invention may be usedas facade lining to insulate a building from the outside. In this case,the mineral foam according to the invention may be coated by a finishingcompound.

The invention also relates to a system comprising the mineral foamaccording to the invention. The mineral foam may be present in thesystem, for example as insulating material. The system according to theinvention is a system capable of resisting to transfers of air and tothermohydric transfers, which is to say that this element has controlledpermeability to transfers of air or water in the vapour or liquid form.

The system according to the invention, which resists to transfers of airand to thermohydric transfers in the construction field, comprises atleast a framework. This framework may be secondary or primary. Thisframework may be of concrete (stud or beam), metal (support or beam),wood, plastics, composite material or a synthetic material. Thisframework may be a metal structure, a stud or a rail.

The system according to the invention may be used to produce a lining,an insulation system or a partition wall, for example a separationpartition wall, a distribution partition wall or an inner partition.

The mineral foam according to the invention may be used to fill hollowparts of building blocs, such as cavity bricks. The foam may be filledinto the cavity at any production step of the building bloc.

The mineral foam according to the invention may be cast verticallybetween two walls, for example between two concrete walls, two brickwalls, two plaster boards, two wood walls, to obtain a system.

The invention will now be described by reference to the following nonlimitative examples.

The following measuring methods were used:

Laser Granulometry Method

In this specification, including the accompanying claims, particle sizedistributions and particle sizes are as measured using a lasergranulometer of the type Mastersize 2000 (year 2008, series MAL1020429)sold by the company Malvern.

Measurement is effected in an appropriate medium (for example an aqueousmedium for non-reactive particles, or alcohol for reactive material) inorder to disperse the particles. The particle size shall be in the rangeof 1 μm to 2 mm. The light source consists of a red He—Ne laser (632 nm)and a blue diode (466 nm). The optical model is that of Frauenhofer andthe calculation matrix is of the polydisperse type. A background noisemeasurement is effected with a pump speed of 2000 rpm, a stirrer speedof 800 rpm and a noise measurement for 10 s, in absence of ultrasound.It is verified that the luminous intensity of the laser is at leastequal to 80% and that an decreasing exponential curve is obtained forthe background noise. If this is not the case, the cell's lenses have tobe cleaned.

Subsequently, a first measurement is performed on the sample with thefollowing parameters: pump speed 2000 rpm and stirrer speed 800 rpm. Thesample is introduced in order to establish an obscuration between 10 and20%. After stabilisation of the obscuration, the measurement is effectedwith a duration between the immersion and the measurement being fixed to10 s. The duration of the measurement is 30 s (30000 analyseddiffraction images). In the obtained granulogram one has to take intoaccount that a portion of the powder may be agglomerated.

Subsequently, a second measurement is effected (without emptying thereceptacle) with ultrasound. The pump speed is set to 2500 rpm, thestirrer speed is set to 1000 rpm, the ultrasound is emitted at 100% (30watts). This setting is maintained for 3 minutes, afterwards the initialsettings are resumed: pump speed at 2000 rpm, stirrer speed at 800 rpm,no ultrasound. At the end of 10 s (for possible air bubbles to clear), ameasurement is carried out for 30 s (30000 analysed images). This secondmeasurement corresponds to a powder desagglomerated by an ultrasonicdispersion.

Each measurement is repeated at least twice to verify the stability ofthe result.

Measurement of the Specific BLAINE Surface

The specific surface of the various materials is measured as follows.The Blaine method is used at a temperature of 20° C. with a relativehumidity not exceeding 65%, wherein a Blaine apparatus Euromatest Sintcoconforming to the European Standard EN 196-6 is used.

Prior to the measurement the humid samples are dried in a drying chamberto obtain a constant mass at a temperature of 50-150° C. The driedproduct is then ground in order to obtain a powder having a maximumparticle size of less than or equal to 80 μm.

EXAMPLES

The method according to the invention was used in order to producemineral foams B, C, E, F and H starting from cement slurries with theslurry formulations II, III, IV, VI and VIII and from aqueous foam 1 and2. Comparative examples have also been realized, namely the mineralfoams A, D and G starting from the cement slurries with the slurryformulations I, IV and VII, in order to illustrate the advantageousaspects of the invention.

Materials Used:

The cements are Portland cements originating from different Lafargecement productions sites, as indicated in Table 1. These cements arestandard type cements. The letters “R” and “N” correspond to thedefinition given in the European NF EN 197-1 Standard, version April2012.

The plasticizer is a mixture comprising a polycarboxylate polyoxide(PCP) from the Chryso company under the brand name of Chrysolab EPB530-017, which does not comprise an anti-foaming agent. The solidscontent of Chrysolab EPB 530-017 is 48 wt.-%

The foaming agents used are the following derivative proteins of animalorigin:

-   -   Propump 26 obtained from the company Propump Engineering Ltd        having a solids content of 26 wt.-%    -   MAPEAIR L/LA obtained for the company MAPEI, having a solids        content of 26 wt.-%.

The different CSH seeds used in the examples are produced by followingthe protocols described above:

-   -   CSH seed (solids content=20.5%)    -   Sludge (solids content=19.5%)    -   Hydrated paste (solids content=16.6%)

Water: Tap Water. Equipment Used: The Rayneri Mixer:

-   -   A Turbotest mixer (MEXP-101, model: Turbotest 33/300, Serial        N°: 123861) supplied by the company Rayneri, which is a mixer        with a vertical axis.

Pumps:

-   -   A pump having an eccentric screw conveyer Seepex™ of the type MD        006-24, commission no. 244920.    -   A pump having an eccentric screw conveyer Seepex™ of the type MD        006-24, commission no. 278702.

Foamer:

-   -   A foamer comprising a bed of glass beads of the type SB30 having        a diameter of 0.8-1.4 mm filled up in a tube having a length of        100 mm and a diameter of 12 mm.

Static Mixer:

-   -   A static mixer comprised of 32 helicoidal elements of the type        Kenics having a diameter of 19 mm and referred to as 16La632 at        ISOJET.

In the following examples, 8 mineral foams were produced. Each cementslurry is referred to by the numbers I to VIII and each aqueous foam isreferred to by the number 1 or 2. The cement foam (mineral foam) asobtained is a combination of one of the cement slurries with one of theaqueous foams.

Preparation of Cement Slurry

TABLE 1 Slurry formulations I II III IV V VI VII VIII Cemen type CEM ICEM I CEM I CEM I CEM I CEM I CEM I CEM I 52, 5N 52, 5N 52, 5N 52, 5N52, 5N 52, 5N 52, 5N 52, 5N Lafarge plant Le Le Le Saint Saint Saint Vald' Val d' Havre Havre Havre Pierre Pierre Pierre Azergues Azergues LaCour La Cour La Cour Water/Cement 0.29 0.29 0.29 0.29 0.29 0.29 0.290.29 (w/w) X (% Na2O eq 0.22 0.22 0.22 0.66 0.66 0.66 0.40 0.40 soluble)Cement (dry 77.45 76.86 76.85 77.40 74.52 76.81 77.44 76.83 wt %) CaCarbonate — — — — — — — — Water (wt %) 22.46 19.24 18.36 22.35 6.0319.18 22.36 19.21 Super-plasticiser 0.17 0.13 0.17 0.26 0.25 0.24 0.200.19 (wt %) CSH (wt %) 3.77 — — — — 3.76 — 3.77 Sedimentation — — — —19.2 — — — sludge (wt %) Hydrated — — 4.63 — — — — — paste (wt %) %CSH/cement 1.00 1.00 5.00 1.00 1.00The chemical composition of the various cement slurries used forcarrying out the invention are presented in Table 1. The cement slurrieshave ben prepared by using the mixer Rayneri Turbotest 33/300, intowhich the liquid components (water, super-plasticiser, CSHcrystallization seeds) have first been introduced. While mixing at 1000rpm, the solid components (cement and all pulverulent components) haveprogressively been added. The cement slurry was then mixed for twoadditional minutes.

Preparation of the Aqueous Foam

An aqueous solution containing the foaming agent has been introducedinto a receptacle. The composition of this aqueous solution of foamingagent (in particular the concentration and the nature of the foamingagent) is reported in Table 2. The aqueous solution of the foaming agentwas pumped by means of a volumetric pump having an eccentric screwconveyor Seed TM MD-006-24 (commission no: 278702).

This foaming agent solution was introduced into the foamer through thebed of beads by means of pressurized air (1-6 bar) and a T-junction. Theaqueous foam was produced in a continuous way at a rate as indicated inTable 2.

TABLE 2 1 2 Foaming agent Propump26 MapeAIR L/LA Concentration (%liquid/water) 3.5 2.5 Concentration (% dry/water) 0.91 0.65 Rate, Air(L/min) 8 8 Rate, Solution (L/min) 0.41 0.41

Preparation of a Slurry of Foamed Cement

The cement slurries as previously obtained have been poured into themixing receptacle while mixing (400 rpm). The cement slurry was pumpedby means of a volumetric pump having an eccentric screw conveyer Seepex™MD 006-24 (commission no: 244920) at a rate of 0.25 L/min.

The pumped slurry and the aqueous foam, continuously prepared, have beenbrought into contact with each other in a static mixer and a slurry offoamed cement was obtained.

Preparation of a Mineral Foam

The slurry of foamed cement was poured into cubes of polystyrene havinga dimension of 10×10×10 cm and into cylindrical columns having a heightof 2.50 m and a diameter of 20 cm. Three cubes have been realized foreach slurry of foamed cement. The cubes have been demoulded after 1 dayand stored 7 days at a relative humidity of 100% and a temperature of20° C. The cubes have then been dried at a temperature of 45° C. until aconstant mass is obtained. A column has been realized for certainslurries of foamed cement. The columns have been demoulded after 3 to 7days and then cut in sections having a length of 25 cm. The sectionshave been dried until a constant mass is obtained.

Analysis of the Mineral Foams

The stability of the foams has been measured by visual inspection of thecubes before demoulding. A foam has been described as “stable”, if thecube kept its height of 10 cm after setting. A foam has been describedas “unstable”, if the cube has collapseed during its setting. Each testwas carried out on 3 cubes of 10×10×10 cm. The results show a similarperformance among the 3 cubes. As the case may be, the results are themean value of 3 cubes.

A column has been considered stable if the density between the lowersection and the upper section does not differ by more than 5 kg/m.

Thermal Conductivity of the Mineral Foams

The thermal conductivity has been measured by means of an apparatus formeasuring thermal conductivity: CT-meter supplied by the companyAlphis-ERE (Resistance 5 Ω, sensor wire 50 mm. The measurements havebeen carried out on dry samples at a temperature of 45° C. until aconstant mass is obtained. The sample is then cut in two equal pieces bymeans of a saw. The measuring sensor was placed between the two surfacesof the sample halves (on the side of the sawing). The heat wastransferred from the source to the thermo element through the materialthat surrounds the sensor; the temperature raise of the thermo elementwas measured as a function of time, which allowed to calculate thethermal conductivity of the sample.

Density of the Mineral Foams

The humid density of the cement slurry was measured by weighing thecubes at the time of casting.

The dry density of the samples was measured on dried samples at atemperature of 45° C. until a constant mass was obtained, while pressingthe cubes.

The Results

The results are presented in Table 3.

TABLE 3 Mineral foam A B C D E F G H Aqueous 2 2 2 2 2 2 1 1 foam SlurryI II III IV V VI VII VIII formulation Density of 110 114 113 106 113 109110 110 mineral foam, humid (g/L) Density of 72 73 69 nm 65 64 — 68mineral foam, dry (g/L) Stability Stable Stable Stable unstable StableStable unstable Stable (cube) Size of >2 1 < x < 2 1 < x < 2 — 1 < x < 31 < x < 2 — 1 < x < 2 bubbles (mm) Stability nm Stable nm — nm Stable —nm (column 16*32) Lambda 0.043 nm 0.041 — nm nm — nm (W/k · m) nm notmeasured unstable means that the foam collapsed

The results show that all foams made from cement slurries that containCSH crystallization seeds (II, III, V, VI and VIII) are stable.

Furthermore, these stable foams have a reduced average diameter of theirair bubbles, which is known to be associated with increased stability ofthe foam.

Furthermore, comparing foams D and E, and the foams G and H, made fromslurries where the only variable is the presence of CSH seeds, showstheir role to generating a stable mineral foam.

1. A process for the production of a mineral foam comprising thefollowing steps: (i) separately preparing a slurry of cement and anaqueous foam, wherein the cement slurry comprises water and Portlandcement as well as calcium silicate hydrate crystallization seeds; (ii)contacting the slurry of cement with the aqueous foam to obtain a slurryof foamed cement; (iii) casting the slurry of foamed cement and leave itto set, wherein the mineral foam is substantially free of particles witha mean diameter D50 <2 μm.
 2. The process according to claim 1, whereinthe calcium silicate hydrate crystallization seeds comprise calciumsilicate hydrate particles.
 3. The process according to claim 1, whereinthe calcium silicate hydrate crystallization seeds are present in theform of an aqueous suspension.
 4. The process according to claim 1,wherein the calcium silicate hydrate crystallisation seeds are presentin an amount of 0.5-7% in dry calcium silicate hydrate by weight ofPortland cement.
 5. The process according to claim 1, wherein the D50 ofbubbles of the aqueous foam prepared in step (i) is less than or equalto 400 μm.
 6. The process according to claim 1, wherein step (ii)comprises the introduction of the slurry of cement and the aqueous foaminto a static mixer to obtain the slurry of foamed cement.
 7. Theprocess according to claim 1, wherein a W/C ratio (wt/wt ratio) of0.28-0.35 is used in step (i).
 8. The process according to claim 1,wherein the Portland cement is a cement of the type CEM I, CEM II, CEMIII, CEM IV or CEM V.
 9. The process according to claim 1, wherein thePortland cement has a specific surface (Blaine) of 3000-10000 cm²/g. 10.The process according to claim 1, wherein the cement slurry comprises awater reducer.
 11. The process according to claim 1, wherein the slurryof foamed cement comprises at least one supplementary mineral component.12. A method comprising utilizing calcium silicate hydratecrystallization seeds for enhancing the mechanical stability and/orreducing the collapse of a slurry of foamed cement, said slurry offoamed cement being obtained by (i) separately preparing a slurry ofcement and an aqueous foam, wherein the cement slurry comprises waterand Portland cement as well as calcium silicate hydrate crystallizationseeds; and (ii) contacting the slurry of cement with the aqueous foam toobtain the slurry of foamed cement.
 13. Use method according to claim12, wherein the calcium silicate hydrate crystallisation seeds arepresent in an amount of 0.5-7% in dry calcium silicate hydrate by weightof Portland cement. 14.-18. (canceled)
 19. The process according toclaim 4, wherein the calcium silicate hydrate crystallisation seeds arepresent in an amount of 0.5-5% in dry calcium silicate hydrate by weightof Portland cement.
 20. The process according to claim 19, wherein thecalcium silicate hydrate crystallisation seeds are present in an amountof 0.7-3% in dry calcium silicate hydrate by weight of Portland cement.21. The process according to claim 9, wherein the Portland cement has aspecific surface (Blaine) of 3500-6000 cm²/g.
 22. The process accordingto claim 10, wherein the water reducer is a plasticiser orsuper-plasticiser.
 23. The process according to claim 11, wherein the atleast one supplementary mineral component is a supplementarycementitious material.
 24. The process according to claim 11, whereinthe at least one supplementary mineral component is selected fromcalcium carbonate, silica, ground glass, solid or hollow glass beads,glass granules, expanded glass powders, silica aerogels, silica fume,granulated blast furnace slags, ground sedimentary siliceous sands, flyash or pozzolanic materials or mixtures thereof.
 25. The methodaccording to claim 13, wherein the calcium silicate hydratecrystallisation seeds are present in an amount of 0.5-5% in dry calciumsilicate hydrate by weight of Portland cement.
 26. The method accordingto claim 25, wherein the calcium silicate hydrate crystallisation seedsare present in an amount of 0.7-3% in dry calcium silicate hydrate byweight of Portland cement.